In two-way radio systems, push-to-talk represents a method of communication in which the talker is required to keep a switch activated while talking. In dispatch call processing, a mobile unit uses a half-duplex link to send voice packets to one or more mobile units. The half-duplex communication mode is referred to as push-to-talk because a button is pushed when transmitting talking and the same button is released when receiving listening. That is, after the user of the first mobile unit depresses the “talk” button, other mobile unit users are prevented from sending packets to other users in the group until the user of the first mobile unit releases the button.
A telephone network employs a full-duplex persistent connection, also known as a circuit, between terminals. In such a system, information is continuously transferred between all communicating terminals. Talk from a user of one terminal, however, does not prevent users at other terminals within a group of terminals from talking to other members of the group at any time during a group conversation or conference. All members of the group in the call are permitted equal access and share the voice channel simultaneously.
Telephone systems utilizing touch tone telephones employ DTMF Dual Tone Multi-Frequency, which assigns two specific frequencies, or tones, to each key so that it can easily be identified. With DTMF, each key pressed on a phone-terminal generates two tones of specific frequencies. These tones are generated when the user depresses a push button on the terminal. The tones are a form of in-band signaling that maybe interpreted for call-processing within a telephone system.
As the need for network interworking becomes more widespread, especially with the deployment of IP networks, there is an increasing need for service providers to interconnect with other networks that are using different signaling protocols. Network providers and operators of radio and telephony networks may employ intermediate systems proxies and call agents which may be used for inter-networking for call routing, call signaling, capabilities exchange, media control, and supplementary services.